The present invention relates to a novel method of preparing SiCO ceramic fibers in which a composition comprising a substantially linear polysiloxane fluid is used as the ceramic fiber precursor.
Small diameter, polymer-derived SiCO ceramic fibers are useful as the reinforcing phase in composite structures. Numerous methods for the preparation of these fibers are known in the art and several are used commercially. The most common approach has been to start with a polycarbosilane polymeric precursor. This precursor, however, presents several difficulties. For instance, the cage-like molecular structure of polycarbosilane makes it difficult to spin. Similarly, the polymer's slow crosslinking and the green fiber's fragility inhibit the use of continuous processing.
The use of polysiloxane resins as precursors to SiCO fibers is also known in the art. For instance, published European Patent Application 435,065 teaches spinning such resins into green fibers, doping the green fibers with boron and pyrolyzing the green fibers to form polycrystalline SiC fibers. These resins, however, are also difficult to spin and the green fibers can be fragile.
The present inventor has now discovered that a composition comprising substantially linear polysiloxanes, as compared to the resins described above, can be easily drawn into fibers. These fibers can be rapidly cured into green fibers which are considerably tougher than those made from resinous precursors and, upon pyrolysis, produce SiCO fibers.